How to Troubleshoot a NORDYNE Furnace That Is Not Getting Oxygen

Replace the air filter on the furnace. A clogged or dirty filter prevents airflow and a new filter often solves the problem entirely. A bad filter may also cause the furnace to short cycle, meaning that it turns on and off in quick succession.

Verify the air circulation blower is running. If it isn't, there may be a short in the system or the blower itself needs replacement.

Turn off the power to the furnace and then check the fuses. The air blower might not work properly because of a blown fuse, which often turn black when they blow out. Replace the fuse and restart the furnace.

Inspect the air inlet for blockages. Cleaning the air inlet helps improve air flow if a clog is to blame.

Listen to the furnace as it starts. If it sounds unusually loud, the gas pressure may be set too high and there isn't enough oxygen to interact with it. The gas pressure needs reduction but this should be done by a trained professional for safety purposes.

Test the pressure switch by pulling the orange wires out of the switch. Hook up a differential pressure gauge to the switch tees. Turn on the furnace motor and check for continuity across the pressure switch using an ohm meter. Replace the pressure switch if the ohm reading shows infinity and the pressure gauge is higher than -.30 inches of water column, or wc. This indicates the pressure switch failed and the system therefore isn't getting appropriate air pressure.